Cyanine dyes are important compounds used as photographic sensitizing dyes, dyes, fluorescent coatings, functional materials (e.g., nonlinear optical materials), pigments, medicines, etc.
It is known that cyanine dyes form aggregates to give an aggregation absorption different from the absorptions assignable to the monomers. In particular, J aggregates are extensively utilized for the spectral sensitization of silver halide photographic materials. In general, however, controlling the aggregates of cyanine dyes is very difficult and the mode of aggregation changes are aggregates into various ones as a result of the influence of dye addition conditions, the compositions of silver halide emulsions, additives, or other factors.
Proposed as a means for enabling a dye aggregate to have only one mode of aggregation is a compound comprising two cyanine dyes connected to each other (hereinafter referred to as a connected-dye compound). Examples thereof include the dye described in Tetrahedron Letter, Vol. 21, pp. 2977-2980 (1980) and the dye described in Dyes and Pigments, Vol. 10, pp. 111-120 (1989).
However, these conventional connected-dye compounds have a problem that the configuration of the connected groups is still unfixed and the same aggregation state cannot always be maintained, or that the mode of connection is different from that of a dye aggregation model (i.e., the structure in which one dye plane is in parallel with and lies over the other).
It has consequently been desired to develop a connected-dye compound having the same configuration as a dye aggregate.